The present invention pertains to: (i) a retroreflective article containing a polyether polyurethane binder layer; (ii) a method of making such an article; and (iii) an article of clothing that displays a retroreflective article.
Retroreflective articles return incident light back towards the light source. This unique ability has promoted widespread use of retroreflective articles on clothing. Persons who work or exercise near motor vehicle traffic need to be conspicuously visible so that they do not get struck by passing motor vehicles. A retroreflective article highlights the person""s presence to motorists at nighttime by retroreflecting light from motor vehicle headlamps. Light from the headlamps strikes the retroreflective article on the wearer""s clothing and is returned toward the motor vehicle, enabling the driver to become aware of the person""s presence. The bright image displayed by the retroreflective article, gives the motorists more time to react.
Retroreflective articles that are displayed on clothing typically comprise a layer of transparent microspheres, a polymeric binder layer, and a specularly reflective layer. The transparent microspheres are partially embedded in the polymeric binder layer, and the specularly reflective layer is disposed behind the microsphere""s embedded portions. Light striking a retroreflective article""s front surface, passes through the transparent microspheres, strikes the specularly reflective layer where it is reflected, and then returns through the microspheres where its direction is altered to travel back in the direction of the light source.
Retroreflective articles that are displayed on clothing must be able to withstand stringent laundering conditions; otherwise, the articles cannot continue to retroreflect light after repeated washings. Investigators in the retroreflective art, therefore, pursue an ongoing goal of developing launderably-durable retroreflective articles so that persons wearing retroreflective clothing can continue to be conspicuously visible after their clothing has been worn and cleaned many times. The United States patents mentioned below illustrate some of the developments in this field.
U.S. Pat. No. 4,763,985 to Bingham discloses a launderable retroreflective article comprising a layer of transparent microspheres, a specular reflective layer optically connected. to each microsphere, and a binder layer into which the microspheres are partially embedded. Resins disclosed as being suitable for use as binder layers include aliphatic and aromatic polyurethanes, polyesters, polyvinyl acetate, polyvinyl chloride, acrylics, or combinations thereof. The specular reflective layers are composed of two succeeding layers of dielectric material.
U.S. Pat. No. 5,200,262 to Li discloses a launderably durable retroreflective article comprising a monolayer of metal-coated microspheres partially embedded in and partially protruding from a binder layer that comprises a flexible polymer having active hydrogen functionality""s and one or more isocyanate-functional silane coupling agents. The flexible polymers that possess active hydrogen functionality""s include crosslinked, flexible, urethane-based polymers such as isocyanate-cured polymers or one or two component polyurethanes and polyols. This retroreflective article provides very good laundering durability: it can withstand industrial laundering conditions, which involve wash temperatures as high as 40 to 90xc2x0 C. (105 to 190xc2x0 F.) and pH values of 10 to 12.5.
U.S. Pat. No. 5,283,101 to Li discloses a launderably durable retroreflective article that comprises a binder layer formed from an electron-beam curable polymer and typically one or more crosslinkers and silane coupling agents. The electron-beam curable polymers include chlorosulfonated polyethylenes, ethylene copolymers comprising at least about 70 weight percent of polyethylene such as ethylene/vinyl acetate, ethylene/acrylate and ethylene/acrylic acid, and poly(ethylene-co-propylene-co-diene) polymers. Glass microspheres are embedded in the cured binder layer, and a specular reflective metal layer is disposed on the microsphere""s embedded portions. This retroreflective article also has been shown to be durable under industrial laundering conditions.
The present invention provides a new retroreflective article that is extraordinarily durable under industrial wash conditions. In brief summary, the new article includes a layer of retroreflective elements at least partially embedded in a binder layer that comprises a polyurethane polymer that is the reaction product of (i) a polyether polyol having a number average molecular weight of at least 2,000 and (i) a polyisocyanate.
In another aspect, the present invention provides an article of clothing that has the inventive retroreflective article disposed on its outer surface. In a further aspect, the invention provides a method of making a retroreflective article, which comprises: partially embedding retroreflective elements in a binder layer that comprises a polyurethane polymer that is the reaction product of (i) a polyether polyol having a number average molecular weight of at least 2,000 and (ii) a polyisocyanate.
The present invention differs from known retroreflective articles in that the binder layer comprises a polyurethane polymer that is derived from a polyether polyol and a polyisocyanate, where the former has a number average molecular weight of at least 2,000. The inventor discovered that this binder layer provides the retroreflective article with enhanced abrasion resistance and excellent laundering durability. The retroreflective articles are able to retain a large percentage of their initial retroreflectivity after repeated washings under industrial conditions. The improved wash performance predictably stems from the resiliency of the binder layer polymer. The resiliencyxe2x80x94it is believedxe2x80x94helps firmly retain the retroreflective elements in the binder layer. This prevents harsh agents from contacting the embedded retroreflective elements and causing their oxidation. Oxidized retroreflective elements are unable to retroreflect light to a significant extent. It is also suspected that the binder layer""s resiliency prevents the retroreflective elements from becoming dislodged from the binder layer.